This invention relates to an improvement in a regulation of a high voltage generated by a high voltage generator used in a picture display apparatus such as a television receiver set using a CRT for picture display.
It is necessary to apply a high voltage as high as about 25 kV to an anode of a picture tube in, for example, a television receiver set. In order to obtain such a high voltage, a flyback pulse voltage appearing in a horizontal retrace period is boosted by a flyback transformer and is then rectified by a diode rectifier.
The pulse top of the flyback pulse waveform can be broadened by selecting the inductances and arrangement of the primary and secondary windings of the flyback transformer so that an equivalent inductance and a stray capacitance of the flyback transformer are tuned with a fifth higher harmonic of the flyback pulse and superposing this fifth higher harmonic on the flyback pulse waveform. When the pulse top of the flyback pulse waveform is so broadened, the conduction angle of the diode rectifier is widened thereby improving the regulation of the high voltage applied to the anode of the picture tube.
As an example of a device which further improves the voltage regulation, U.S. Pat. No. 4,112,337 discloses a high voltage generator in which an LC parallel resonance circuit tuned with a higher harmonic of a flyback pulse is inserted in series with a primary winding of a flyback transformer. This resonance circuit attenuates the higher harmonic of the flyback pulse thereby flattening the top of the flyback pulse waveform. This pulse waveform having the flattened top is boosted by the flyback transformer and is then rectified by a diode. Therefore, the conduction angle of the diode is windened to further improve the regulation of the high voltage.
However, the LC parallel resonance circuit disclosed in the U.S. Patent cited above is still defective in that an increase in the load results in a voltage drop since the flyback pulse waveform is maintained constant regardless of any variation of the load and that the voltage decreases by an amount corresponding to the degree of attenuation of the higher harmonic by the resonance circuit.